CVE-2025-7613: Totolink T6 Firmware RCE Vulnerability

CVE-2025-7613 Overview

CVE-2025-7613 is a command injection vulnerability in the TOTOLINK T6 router running firmware version 4.1.5cu.748. The flaw resides in the CloudSrvVersionCheck function of /cgi-bin/cstecgi.cgi, which is part of the HTTP POST request handler. Attackers can manipulate the ip argument to inject arbitrary operating system commands. The issue is classified under [CWE-74] (Improper Neutralization of Special Elements in Output Used by a Downstream Component) and is reachable over the network. Public disclosure of the exploit technique has occurred through third-party vulnerability research repositories.

Critical Impact

Remote attackers with low-level privileges can execute arbitrary commands on affected TOTOLINK T6 routers by sending crafted HTTP POST requests to the cloud service version check endpoint.

Affected Products

• TOTOLINK T6 router (hardware)
• TOTOLINK T6 firmware version 4.1.5cu.748_b20211015
• Deployments exposing the /cgi-bin/cstecgi.cgi interface to untrusted networks

Discovery Timeline

• 2025-07-14 - CVE-2025-7613 published to the National Vulnerability Database
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-7613

Vulnerability Analysis

The vulnerability exists in the CloudSrvVersionCheck handler exposed through /cgi-bin/cstecgi.cgi on the TOTOLINK T6 router. This endpoint processes HTTP POST requests intended to verify cloud service version information. The handler accepts an ip parameter from the request body and passes the value to a downstream system command without proper neutralization of shell metacharacters. An authenticated attacker on the network can craft a POST request that embeds shell command separators within the ip field. The injected commands execute in the context of the CGI process, which typically runs with elevated privileges on embedded router firmware. Successful exploitation grants control over device configuration, network traffic, and connected client communications.

Root Cause

The root cause is improper input sanitization within the CloudSrvVersionCheck function. The firmware concatenates the attacker-controlled ip argument into a shell invocation, likely to perform a connectivity check against a cloud server. Because the argument is not validated against a strict IP address format and shell metacharacters are not filtered, special characters such as semicolons, backticks, and pipes are interpreted by the underlying shell.

Attack Vector

Exploitation requires the attacker to reach the router's HTTP management interface and to hold valid low-privilege credentials. The attacker sends an HTTP POST request to /cgi-bin/cstecgi.cgi with a JSON body invoking the CloudSrvVersionCheck topic. The ip value contains a benign address followed by a shell separator and the injected command payload. The router's CGI process evaluates the combined string through the system shell, executing the attacker's commands. Detailed proof-of-concept content is available in the GitHub Vulnerability Report and tracked under VulDB #316313.

Detection Methods for CVE-2025-7613

Indicators of Compromise

• HTTP POST requests targeting /cgi-bin/cstecgi.cgi containing the CloudSrvVersionCheck topic with shell metacharacters such as ;, |, &, or backticks in the ip parameter.
• Outbound connections from the router to unexpected hosts following requests to the CGI endpoint.
• Unexpected processes spawned by the cstecgi.cgi parent on the device, including shell utilities like sh, wget, or nc.
• New or modified accounts, cron jobs, or startup scripts on the router's filesystem.

Detection Strategies

• Inspect HTTP request bodies bound for the router's management interface and alert on shell metacharacters within parameters expected to contain IP addresses.
• Baseline normal cstecgi.cgi traffic patterns and flag anomalous POST volumes or payload sizes.
• Correlate router-originated DNS lookups and outbound TCP sessions against threat intelligence feeds for command-and-control infrastructure.

Monitoring Recommendations

• Collect syslog and HTTP access logs from the router into a centralized analytics platform for retrospective hunting.
• Monitor network segments that contain TOTOLINK T6 devices for lateral movement attempts originating from the router itself.
• Track firmware version inventory and alert when devices running 4.1.5cu.748 remain unpatched.

How to Mitigate CVE-2025-7613

Immediate Actions Required

• Remove the router's web management interface from any untrusted network and restrict access to a dedicated management VLAN.
• Rotate administrative credentials and disable any unused or default accounts that could be used to reach the vulnerable endpoint.
• Block external access to /cgi-bin/cstecgi.cgi at the network perimeter until a vendor fix is applied.
• Audit the device for signs of prior compromise, including unfamiliar processes, configuration changes, and DNS settings.

Patch Information

At the time of NVD publication, no vendor patch URL was listed in the advisory references. Administrators should monitor the TOTOLINK security page for firmware updates that address the CloudSrvVersionCheck command injection. Until a fixed firmware build is published, the device should be treated as exposed.

Workarounds

• Disable remote (WAN-side) administration on affected TOTOLINK T6 devices.
• Place the router behind an upstream firewall that filters POST requests containing shell metacharacters in the ip field.
• Replace end-of-life or unpatched units with a supported model if the vendor does not release a firmware update.